1. Field of the Invention
This invention relates to an ejector (refer to JIS (Japanese Industry Standard) Z 8126, No. 2.1.2.3.) that is pressure reducing means, for reducing a pressure of a fluid, and a momentum transportation type pump for transporting the fluid by entrainment with an operation fluid jetted at a high speed. The ejector is effective when applied to a refrigerator, an air conditioner, etc, employing the ejector as pressure reducing means for reducing a pressure of a coolant and as pump means for circulating the coolant.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2003-185275 describes an ejector that is used as coolant pressure reducing means and as coolant circulating means and regulates a flow rate of the coolant passing through the ejector.
In the ejector 50 of this prior art example shown in FIG. 4, the coolant pressurized to a high pressure by a compressor flows into a high pressure space 18 through an inlet 51. As a throttle portion 17c of a nozzle 17 contracts a passage area, pressure energy of the high pressure coolant is converted to velocity energy. The coolant is thus accelerated and is jetted from a jet port 17b. A gaseous phase coolant evaporated in an evaporator is sucked from a gaseous phase coolant inlet 22a by entrainment with the flow of the jetted coolant having a high speed.
The coolant further passes through a mixing portion 23 and flows into a diffuser portion 24. The ejector converts expansion energy of the coolant to pressure energy in this diffuser portion 24, elevates the pressure of the coolant on the suction side of the compressor and reduces power consumption of the compressor on the downstream side of the flow of the coolant. After passing through the diffuser portion 24, the coolant is separated by a gas-liquid separator into a liquid phase coolant and a gaseous phase coolant. The gaseous phase coolant is sucked into the compressor and the liquid phase coolant evaporates in the evaporator, changes to the gaseous phase coolant and reaches the gaseous phase coolant inlet 22a. 
In the prior art example, the needle valve 19 is caused to undergo displacement in an axial direction R (in a transverse direction in FIG. 3) of the nozzle by displacement means 52 to change the opening of the throttle portion 17c, that is, the opening of the nozzle 17 (flow passage area through which the coolant can flow) and can thus increase or decrease the flow rate of the coolant passing through the nozzle 17. In this prior art example, when the needle valve 19 undergoes displacement in a jet port direction R1 (to the right in FIG. 3), the opening of the nozzle 17 is decreased and when the needle valve 19 undergoes displacement in a direction R2 opposite to the jet port (to the right in FIG. 3), the opening of the nozzle 17 is increased.
This ejector 50 can increase the opening of the nozzle 17 when the compressor turns at a high speed, that is, when the amount of the coolant flowing into the ejector 50 is great, and can increase the amount of the coolant flowing through the nozzle 17 (ejector 50). Because the amount of the coolant flowing through the evaporator downstream of the ejector 50 in the coolant flowing direction thus increases, the refrigeration (cooling) capacity can be improved particularly when the amount of the coolant flowing through the cycle is large in comparison with the case where the flow rate of the coolant passing through the ejector 50 cannot be increased or decreased.
The inventors of the present invention have examined an ejector 53 of a comparative example using a solenoid 20 shown in FIG. 4 as a general method of causing displacement of the needle valve 19. This comparative example includes a partition 54 so arranged as to slidably support the needle valve 19 in the axial direction R of the nozzle. Because the partition 54 is disposed at a position that separates a high pressure space 18 from an opposite side end portion space 21 at which an end portion 19c of the needle valve 19 opposite to the jet port is positioned, a communication passage 54a communicates both spaces 18 and 21 with each other so that the pressures inside both spaces 18 and 21 are substantially the same. Consequently, the needle valve 19 is concretely allowed to undergo displacement in the axial direction R of the nozzle.
In the needle valve 19 of the ejector of the comparative example, however, the pressure difference between the opposite side end portion 19c opposite to the jet port (high pressure) and the jet port side end portion 19b (low pressure) is large in the needle valve 19. Therefore, the needle valve 19 receives force (drag) in the jet port direction R1 (to the right in FIG. 4) and large force is necessary for the displacement of the needle valve 19. Consequently, problems occur in that the solenoid 20 becomes large and delicate displacement in the axial direction R of the nozzle is difficult particularly when the flow rate is small.